#include<stdio.h>
#include<math.h>
int main()
{
int i;
int n;
double den = 1.0;
double num = 0.0;
double pen = 1.0;
double figh = 1.0;
scanf("%d",&n);
for(i = 1; i <= n;i ++)
{
num += (figh * i) / den;
den += 2;
figh = -figh;
}
printf("%.3lf",num);
return 0;
}
